Osmunda claytoniana , Z., ( 9 . cinnamomea , Z. 77 
glossum , Equisetum , and Isoetes , and strengthens the view 
that the concentric bundle is a secondary and not the primary 
form among the Filicineae. 
Cross-sections of the young lamina show a better marked 
epidermis on both sides than is found in the petiole. These 
are separated usually by two layers of mesophyll-cells. Toward 
the margin these are in close contact, as they are throughout 
in the very young leaf, but as the lamina expands, large inter- 
cellular spaces arise between them. Stomata are present on 
both surfaces, but their development was not followed. The 
fibro-vascular bundles are of the same type as those of the 
petiole, but are smaller. 
The main difference observed in the cotyledons of the two 
species examined was the colour. This in O. claytoniana is 
a very light, yellowish green, while in O. cinnamomea it was 
much darker. This difference also exists, as before noted, in 
the prothallium. 
The Stem .— The stem arises from the upper epibasal 
quadrant, as usual, and its early divisions correspond closely 
to those in the leaf-quadrant. The first segment in the 
octant that becomes the apical cell, seems to be always turned 
toward the basal wall, and growth in this octant is stronger, 
so that the apical cell very soon comes to lie almost exactly in 
the axis of the embryo, and its direction of growth is coin- 
cident with it. As the growth of the cotyledon tends more 
and more upward, it soon forms almost a right angle with the 
stem. 
At first the four faces of the tetrahedral apical cell are 
almost equal, but in the older embryo, the lateral faces are 
deeper (Fig. 99). The segments are cut off slowly and the 
apex of the stem projects but slightly. As in the cotyledon, 
the first wall in each segment divides it into an inner and an 
outer cell : from the former the plerome arises, from the 
latter dermatogen and periblem. Whether each segment gives 
rise to a leaf, I cannot state, as the development of the embryo 
was not followed beyond the second leaf which arises, in part 
at least, from the inner stem-octant. 
